High quality, precisely controlled capacitors are an integral part of many semiconductor devices. Capacitors are fabricated as part of a semiconductor circuit by using the Metal Oxide Silicon (MOS) system. One particular use of semiconductor capacitors is in an integrated circuit whose function is the conversion of analog signals to digital representation. The analog-to-digital conversion is accomplished by a sequential comparison of a signal with fractions of a reference voltage. The reference is divided by applying the comparison through an array of capacitors having capacitances that are successively reduced by factors of two. For an analog-to-digital conversion circuit to function properly, the capacitors in the circuit must be precisely controlled over the entire capacitance value of the circuit. This is accomplished by placing an oxide, such as silicon oxide, over the semiconductor and then fabricating an electrode over the oxide in order to form the capacitor.
Another use for semiconductor capacitors is in applications requiring voltage variable capacitors (VVC) also known as varactors. Currently, varactors are used as voltage variable capacitors to tune the center frequency of electrical networks consisting of resistors, inductors, and capacitors. Varactors with large capacitance per unit area, large capacitance change, and low DC leakage currents are necessary to increase the dynamic range and efficiency of tuned resonators while using lower control voltages. In order to achieve these requirements, high performance VVC's must be used as discrete components in a hybrid package because the currently available high performance VVC's are not compatible with the MOS fabrication process. The performance of the varactor is limited by the electrical characteristics of the insulator, silicon oxide, used in conventional art VVC's. In order to achieve the necessary performance increase, an increased capacitance range must be realized. It would be highly advantageous if the dielectric material would be compatible with the MOS processing and also with bipolar processing schemes.